Imagine it's 1900, and you're a bioethicist. Of course, "bioethics" didn't exist back in 1900--we had real academic disciplines in those days--but play along: You're sitting on a presidential bioethics commission, and scientists show up to testify that a new thing called vaccination could increase life spans by 30 years. Would you judge vaccination unethical? Would you worry about "potentially devastating impacts on the economy, family, and generational relationships"?

If you wouldn't have objected back in 1900, then you can't object in 2008 to the changes being offered by biotechnology. Or so claims Ronald Green in Babies by Design. According to Green, those who object to some of today's biotechnological innovations are engaged in "status-quo bias rather than reasoned reflection." Reasoned reflection, according to Green, tells us to make "deliberate interventions in our own and our children's genetic markup--to both prevent disease and enhance human life."

Consider another thought experiment. What would have happened had our ape ancestors, millennia ago, decided that their genome was best and did what they could to preserve it, preventing further enhancement? If we don't think the ape genome was best, why should we think our current genome is best?

This just-suppose device appears in John Harris's Enhancing Evolution, another new volume which insists that concerns about the possibly dehumanizing effects of some biotechnologies are unwarranted. Harris asks, why wait for Mother Nature to improve us? Why not improve ourselves? Indeed, he argues, "there is a positive moral duty to enhance." He longs for the day when we replace "natural selection with deliberate selection, Darwinian evolution with 'enhancement evolution'" and anyone who thinks otherwise is "like our imagined ape ancestor who ... thought evolution had gone far enough."

Yet another new book, Russell Korobkin's Stem Cell Century, uses the same device. In it, the dean of the Harvard Medical School tells Korobkin that stem cell therapies "have the potential to do for chronic diseases what antibiotics did for infectious diseases." If you don't object to penicillin, then you can't object to the coming "penicillin for Parkinson's." Phrased like that, who could object?

There's something revealing in these new books. They all argue that we have a moral imperative to enhance ourselves, and none of them seriously confronts the concerns that many thoughtful people have about the moral hazards of trying to design a more perfect human. They want to keep the technologies safe and their applications just, to be sure; but they consider these challenges to be easily surmountable. It's as if we've discovered unqualified human goods. Or as Harris puts it, "enhancements are so obviously good for us that it is odd that the idea of enhancement has caused, and still occasions, so much suspicion, fear, and outright hostility."

John Harris is no fringe figure. He's professor of bioethics at the University of Manchester and editor in chief of the prestigious Journal of Medical Ethics. Green, too, belongs to the mainstream. He is a Dartmouth ethics professor and the founding director of the NIH's Office of Genome Ethics. Korobkin has fewer obvious credentials--admitting on his website that he's been researching stem cells only "for the last two years"--but he is a respectable professor at the respected UCLA School of Law.

The surprisingly unsurprising similarity among these authors is that they consistently present inaccurate, strawman versions of opposing arguments. Green, for example, dismisses most opposition out of hand--since, after all, "research has repeatedly shown that human beings resist change, even when there is no good reason to do so." Perhaps Green's whatever-we-decide liberalism, like Harris's libertarian utilitarianism, is simply too shallow to produce penetrating arguments or insights.

This should be the first warning sign to anyone sitting on the fence. On one side of the debates are some of the world's most thoughtful scholars: The University of Chicago's Leon Kass, Harvard's Michael Sandel, Johns Hopkins's Francis Fukuyama, and the German philosopher Jürgen Habermas have different political philosophies and different views on bioethical questions, but all recognize that the issues raised by some new biotechnological possibilities are profound and difficult. On the other side are people who see no serious moral issues anywhere in the neighborhood of biotechnology. Why is creating designer babies ethical? Because they'll be free of disease, and who can be against that? Why are genetic enhancements a good idea? Because they'll make us better--and after all, Harris points out, "If it wasn't good for you, it wouldn't be enhancement."

Yet even when their arguments are more substantial, their materialism and utilitarianism are fatally short-sighted. Much of human fulfillment is social, and we have to consider not just material consequences but how certain biotechnologies may transform the social practices and understandings that contribute to our flourishing. For that matter, some moral principles should guide our research, irrespective of the consequences, and we have to consider what type of respect is due human beings simply because of their humanity.

Much genetic therapy will be good, curing a host of genetic diseases. The problem is that it will not be limited to repairing, and not all enhancements will truly enhance. When scientists found that they could treat muscular dystrophy by genetic therapy, healthy athletes began clamoring to use it. But when do therapies become enhancements? Almost all bioethicists think the distinction is largely meaningless. Harris argues that "the overwhelming moral imperative for both" is to "prevent harm and confer benefit." The result, Green claims, is that these therapies could "narrow the gap between society's haves and have-nots and between developed and developing nations" as they "rectify inequalities of birth." History, however, gives us little reason to suppose he is right.

These books assume a kind of unproblematic Eden awaits us on the far side of biotechnology. Harris predicts parents will "avoid the risk of the genetic roulette that is sexual reproduction." Once all of the options to ensure a genetically healthy child are available, he asks, "could it be ethical not to be a designer?" The end result, Green explains, will be a "world where sex is for fun and reproduction usually takes place in the laboratory." Insisting that "parental love almost always prevails," he does not take seriously the possible consequences for our self-understandings and social practices. What attitude is society likely to adopt towards children when they are manufactured in laboratories? Will people tend to start viewing offspring as a type of property owned by those who paid for them to be produced? Will strict quality controls be put into place and enforced, as with other products of manufacture? What will be the fate of defectives who, somehow, make it through the production process?

And there is more: Might laboratory reproduction undermine the bonds of marriage and the generational ties between mothers (and fathers) and their children? But the real counterargument isn't consequentialist; it is based on the act, the habits of mind and being, and the virtues and vices involved in viewing another human being as an object of technical manufacture. Witness Harris's defense of gender design: "Just as when I choose a designer shirt or dress I am indulging my taste in some directions at least, so it is with gender choice." Should we mention here that kids aren't designer attire? The problem is that Harris and Green ignore the question of whether human beings possess an intrinsic dignity--a dignity that requires that they be treated as personal subjects (and not manufactured objects) who are brought into the world through a union of parents (not the technical fabrication of scientists).

And then there's the question of what type of enhancements we're likely to make. Do we trust ourselves to know what the ideal designer baby actually is? Libertarians don't trust planned economies; should we plan genomes? Environmentalists don't want to alter the natural ecosystem; should we alter the human organism? While isolated acts of cosmetic enhancement (height, gender, breast size, face, etc.) may improve someone's lot in life, their widespread use will transform our social structures while feeding our baser desires and perpetuating prejudices. What effect will widespread enhancement use have on the disabled, the diseased, the unenhanced, and the dying? Since much of our flourishing is social, considering the broad social effects is imperative.

Yet all three of these titles dismiss these reservations as religious drivel. They need the objections to be religious so they can treat them as illegitimate grounds for public policy. But in fact, the leading voices in opposition to genetic engineering all make secular arguments, and Green has to invent his own pseudo-theology to find a counterexample: "We may smile, but for many people the risk of provoking God's anger by genetic engineering is anything but funny." Harris is no better, as he claims religious thinkers argue that "it is tempting fate or divine wrath to play God and intervene in the natural order." But he, too, cites no one who makes these claims. Is any of this true? The late Pope John Paul II taught that genetic therapy should be "considered in principle as desirable, provided that it tends to real promotion of the personal well-being of man, without harming his integrity or worsening his life conditions." Amazingly, Green cites this, yet persists in his provoke-God's-anger rhetoric.

Meanwhile, Korobkin asserts that respect for the human embryo "is rooted in religious belief that by its very nature cannot be contradicted with analytical reasoning" as he argues that the embryo "lacks every trait that could plausibly be considered a characteristic of human moral value except one: it has human DNA." Harris argues that "if the zygote has value because of its potential to become a person, then whatever has the potential to become a zygote [sperm, egg, skin cells via cloning] shares whatever importance the zygote has."

But the counterargument is not that the human zygote is a potential human being, but a human being--a living member of the species Homo sapiens in the earliest stage of his or her natural development. Where sperm and egg are parts of larger organisms, the embryo is a whole organism that will develop by an internally directed process toward adulthood. Precisely because of what the embryo is now--an embryonic human being--we can confidently predict how it will develop and what its mature stage will be.

Harris concedes that embryos and fetuses may be human beings, but argues that they are not persons. Persons are "capable of valuing their own existence," which excludes "embryos, fetuses, and neonates." That's right: Until "neonates"--newborns, infants--can value their own existence, they merit no protection. Most people will find this doctrine, that some human beings are nonpersons, repellant.

So where are we left? "Never before in history have we had anything like this ability to shape the biological inheritance of our children," Green insists--which does rather undo his thought experiment about the 1900 bioethicist. In fact, never before have we had the potential to get things so wrong. One need not agree with Leon Kass, in whole or in part, to think that he deserves something better than -Harris's refutations: "This is pure Humpty Dumpty!" and "Well, whatever turns you on, Leon."

Sadly, these volumes seldom rise above such levels of discourse, and all three will leave most readers dissatisfied. At the end of Stem Cell Century, Korobkin declares that his "conclusion requires abandoning ... the Kantian imperative ... and adopting a utilitarian form of analysis." In his mind, it's either Kant or Jeremy Bentham. Green closes Babies by Design by proposing that enhancements for designer babies should not "increase unjust inequality and discrimination" but should be "aimed at what is reasonably in the child's best interest." A college sophomore could offer this same advice on a moment's reflection; the real question is what precisely counts as the best interests of the child and society.

Harris's Enhancing Evolution also concludes with ethical principles--or principles which people who don't like biotechnology can be ordered to obey. He stresses that there is a "clear moral obligation to participate in medical research"--an obligation that can be coerced. Comparing research to jury duty, he writes: "If compulsion is justifiable in the case of due process, the same or indeed more powerful arguments would surely justify it in the case of science research." At one point, Green writes that he is "struck by how fast the science is moving." And so he should be--for, curiously, all three books appeared as the field of biotech research was changed by the announcement of a way to produce, from skin cells, embryonic-like stem cells without destroying (or even using) embryos.

The main failing here is symptomatic of much modern bioethical thought: These three works assume that human fulfillment consists only in physical and material perfection. Little attention is paid to the virtues and social practices that make for a life well lived. This is true even when Green asserts that biotechnology will "remedy not only physiological imperfections but also some of the serious moral and spiritual problems facing the world community." Really? This would be a more reassuring comment if anything else in Green's pages demonstrated an inclination toward moral reflection. If we can take anything away from thought experiments that transport us back to earlier days, it should be an emphasis on promoting lives of virtue.

Ryan T. Anderson, assistant editor at First Things, is a Phillips Foundation fellow and assistant director of the Program in Bioethics at the Witherspoon Institute in Princeton, N.J.